water.nbhm

Class ConcurrentAutoTable

java.lang.Object

water.nbhm.ConcurrentAutoTable

All Implemented Interfaces:

java.io.Serializable

public class ConcurrentAutoTable
extends java.lang.Object
implements java.io.Serializable

An auto-resizing table of longs, supporting low-contention CAS operations. Updates are done with CAS's to no particular table element. The intent is to support highly scalable counters, r/w locks, and other structures where the updates are associative, loss-free (no-brainer), and otherwise happen at such a high volume that the cache contention for CAS'ing a single word is unacceptable.

This API is overkill for simple counters (e.g. no need for the 'mask') and is untested as an API for making a scalable r/w lock and so is likely to change!

Since:

1.5

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
ConcurrentAutoTable()

Method Summary

Methods

Modifier and Type	Method and Description
void	add(long x) Add the given value to current counter value.
void	decrement() add(long) with -1
long	estimate_get() A cheaper get().
long	get() Current value of the counter.
void	increment() add(long) with +1
int	internal_size() Return the internal counter striping factor.
int	intValue() Same as get(), included for completeness.
long	longValue() Same as get(), included for completeness.
void	print() A more verbose print than toString(), showing internal structure.
void	set(long x) Atomically set the sum of the striped counters to specified value.
java.lang.String	toString() Return the counter's long value converted to a string.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

ConcurrentAutoTable

public ConcurrentAutoTable()

Method Detail

add

public void add(long x)

Add the given value to current counter value. Concurrent updates will not be lost, but addAndGet or getAndAdd are not implemented because the total counter value (i.e., get()) is not atomically updated. Updates are striped across an array of counters to avoid cache contention and has been tested with performance scaling linearly up to 768 CPUs.

decrement

public void decrement()

add(long) with -1

increment

public void increment()

add(long) with +1

set

public void set(long x)

Atomically set the sum of the striped counters to specified value. Rather more expensive than a simple store, in order to remain atomic.

get

public long get()

Current value of the counter. Since other threads are updating furiously the value is only approximate, but it includes all counts made by the current thread. Requires a pass over the internally striped counters.

intValue

public int intValue()

Same as get(), included for completeness.

longValue

public long longValue()

Same as get(), included for completeness.

estimate_get

public long estimate_get()

A cheaper get(). Updated only once/millisecond, but as fast as a simple load instruction when not updating.

toString

public java.lang.String toString()

Return the counter's long value converted to a string.

Overrides:

toString in class java.lang.Object

print

public void print()

A more verbose print than toString(), showing internal structure. Useful for debugging.

internal_size

public int internal_size()

Return the internal counter striping factor. Useful for diagnosing performance problems.